The present invention relates to linear motors and, more specifically, to apparatus for guiding and supporting a movable element of a permanent magnet linear motor in a machine tool.
Linear motors conventionally are used in applications requiring the application of modest force along a linear axis. One application, disclosed in U.S. Pat. No. 4,595,870, for example, includes driving one axis of a positioning table for displacing a workpiece along the axis. Such applications are characterized by high precision in positioning, and modest force and acceleration requirements. The linear motor eliminates the windup characteristic of ball-screw drives and substantially reduces the mass of the moving element. Both of these characteristics of linear motors provide benefits in workpiece positioning precision and acceleration.
The force of which linear motors are capable is limited by resistive heating in the windings of the armature of the linear motor. In my U.S. patent application Ser. No. 859,915, I disclose several techniques for cooling a linear motor. In cooling techniques using liquid coolant, I have discovered that it is possible to attain high forces in permanent magnet DC linear motors using a moderate flow of a liquid coolant in thermal contact with the armature windings. The attainable high force permits such linear motors to be used in applications not previously considered for this a class of motors.
In my U.S. Pat. No. 4,505,464, I disclose a positioning table which takes advantage of the magnetic attraction between permanent magnets and armature iron for preloading bearing supporting the movable element of the positioning table. Two sets of magnets in orthogonal planes provide bi-directional preloading.
In my U.S. patent application Ser. No. 015,680, I disclose a high-force linear motor adapted for integration into the bed of a machine tool. Certain machine-tool applications require very long travel at high speeds and accelerations. The present invention addresses one such application wherein, in addition to the foregoing requirements, long linear axes must be accommodated.